Law enforcement sources tell us YB was picked up after his ex-gf reported the rapper texted her the threat on Wednesday … then showed up at her apartment, kicked down the door, but left without disturbing anything inside.

Cops arrested him on Thursday. He was in custody for a few hours before being released on a $5k bond.

Here’s the kicker, no pun intended, Young Buck is on federal probations.

So unless his lawyer is a wizard of finesse, he’s probably going back to jail on a parole violation sooner than later.
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Photo: TMZ